(1) Field of the Invention
The present invention relates to an optical disk which stores information signals recorded with a light beam and to a reproduction apparatus for reproducing such optical disks, more specifically to an optical disk which stores multimedia data including digital moving picture data, audio data, and sub-picture data and to an optical disk reproduction apparatus for reproducing such optical disks.
(2) Description of the Prior Art
Of conventional optical disks, compact disks (CDs) and video CDs are representative. About an hour of audio digital data can be recorded in a CD, and CDs are used mainly for music software titles. On the other hand, video CDs hold about an hour of moving picture digital data including audio digital data, and are used mainly for movie software titles. CDs and video CDs are prevalent among many music lovers and movie lovers since they are handy and have good quality of sounds and pictures.
As a new fashion in the moving picture software, interactive software titles for video CDs are often seen in the market recently. The interactive software selectively reproduces a plurality of moving pictures stored in an optical disk according to user instructions and dynamically changes reproduction orders during reproductions. An example of such interactive software titles is a multi-story drama in which a story develops according to user selected options.
Now, an optical disk for achieving the interaction and a reproduction apparatus for reproducing the optical disk are described with reference to FIGS. 1A-1C, supposing the optical disk is a video CD. FIGS. 1A-1C show a video CD. The video CD stores a multi-story detective story. Note that a multi-story can develop to a plurality of stories.
FIG. 1B shows how digital data is stored in a video CD. The drawing shows five pieces of moving picture digital data, moving pictures #1-#5, and a group of pieces of reproduction route data for specifying the reproduction order of the moving pictures are stored in the video CD. The digital data sequences making up the moving pictures are stored in the respective consecutive areas in separately. Note that all the digital data sequences need not be stored in the consecutive areas.
FIG. 1A shows the contents of the moving pictures and the reproduction order of them. Moving picture #1 shows an image of a detective entering a room. Moving picture #2 shows a pen and glasses on a desk in the room. Moving picture #3 is a menu providing two option items, item "1" for glasses and item "2" for a pen. Moving picture #4 is reproduced when "1" is selected; moving picture #5 when "2" is selected.
FIG. 1C shows several pieces of reproduction route data. The reproduction route data is divided into two types; one provides a reproduction order for a plurality of moving pictures; the other provides a plurality of branch targets.
The former type is called a play list. In the play list, a plurality of moving pictures to be reproduced successively and the reproduction order are specified. Also, the play list includes a piece of link information which specifies a branch destination of the play list itself, connecting a reproduction route to another.
The latter type is called a selection list. The selection list includes a plurality of reproduction routes as branch target candidates and a menu address. The menu address is a record address for a menu image that provides a plurality of branch targets. The menu image includes a plurality of items whose identification numbers correspond to identifiers of reproduction routes as the branch targets.
In FIG. 1C, reproduction route data #1, #3, and #4 are play lists, and reproduction route data #2 is a selection list. The identifiers of the respective items correspond to numeral keys on a remote controller. If the user presses any of the numeral keys, a corresponding reproduction route is reproduced.
Now, a reproduction of the video CD shown in FIG. 1B is described.
The reproduction apparatus calculates a record address of the starting reproduction route data of the optical disk by using a certain calculation method. On calculating the record address, the reproduction apparatus moves the pickup to a position specified by the address and reads the reproduction route data onto an internal memory. Suppose reproduction route data #1, a play list, is read onto a memory. Then, the reproduction apparatus determines moving pictures to be reproduced according to the reproduction order indicated by the reproduction route data #1. On determining the moving pictures, the reproduction apparatus moves the pickup to a position specified by the record address of the moving pictures and reads the digital data of the moving pictures. The reproduction apparatus converts the digital data into picture output signal and audio output signal through a certain signal process, then outputs the signals to the display and speakers.
After the above processing, the scene of moving picture #1 as shown in FIG. 1A is reproduced for several seconds. Moving picture #1 is followed by moving picture #2, the scene of a desk. The screen displays a pen and glasses for several seconds. When all the moving pictures included in the reproduction route data are reproduced, the reproduction apparatus refers to the link information and reads the next reproduction route data onto a storage through the pickup. Then, the reproduction apparatus discards reproduction route #1 and optically reads the next reproduction data onto the internal memory. As a result, reproduction route data #2 is read onto a memory, and a menu image providing a plurality of branch targets is displayed. Moving picture #3, a menu providing item "1" for glasses and item "2" for a pen, is displayed.
When the user presses a numeral key on a remote controller corresponding to the identifier of an item in the menu, the reproduction apparatus determines a piece of reproduction route data which is the branch target corresponding to the numeral. Then, the reproduction apparatus discards reproduction route #2 and optically reads the determined piece of reproduction data onto the internal memory. In the present example, reproduction route data #3 is read onto a memory if the user selects item "1;" reproduction route data #4 if the user selects item "2."
The reproduction apparatus continues the reproduction according to the new reproduction route data stored in the memory. If reproduction route data #3 is stored in the memory, moving picture #4, an image of close-up glasses, is reproduced. If reproduction route data #4 is stored in the memory, moving picture #5, an image of close-up pen, is reproduced. In this way, the reproduction apparatus continues the reproduction of the moving pictures changing the route according to the selections by the user for the menus. It would be understood that a story in the interactive software can develop in various ways, and that the user can enjoy the multi-story feeling as if he/she is the detective appearing on the screen.
The data used for controlling the reproduction proceeding such as the reproduction route data is called navigation control data. Recently, the format of the navigation control data and the method the reproduction apparatus uses the data are recognized as very important technical subjects. This is because the format determines the capacity of the memory in the reproduction apparatus required for achieving the interactive software. The greater is the memory capacity, the more cost is required for the memory, increasing the price of the reproduction apparatus.
CD players and video CD players, being made for private use, generally use memories with the capacity of several-tens KB or under for achieving low costs. The above interactive software title causes the reproduction apparatus to have a piece of reproduction route data resident in a memory for reproducing a moving picture. The piece of reproduction route data occupies the space of hundreds of bytes in the memory. That means the data does not cause a problem to the reproduction apparatus using a memory having capacity of several tens of KB for reproducing the interactive software title.
Software title creators and users desire interactive software titles having more satisfying performances. They sometimes talk about the limitation in video CDs for achieving such satisfying performances. Now, the functions that cannot be achieved in video CDs and the obstacles to the achievement of such functions are described below.
First problem is that it is impossible to display options of branch targets to allow the user to selects an option in about 2.0 to 3.0 seconds while an image is displayed on the screen. For example, imagine a case where scenes seen from the train window are displayed consecutively on the screen and a set of options are displayed along with a scene of a building such as a castle and a bridge. Since a set of options for video CDs are specified for a whole moving pictures, but not for a part of the moving pictures. If a software title creator desires to realize a specification for a part of the moving pictures, the software title creator must divide the whole moving pictures into small units and specify the sets of options for the small units. However, this arrangement causes the reduction in response. That is, the reproduction of the moving pictures is temporarily stopped due to the disk seek for changing the moving pictures and reproduction route data. Due to the great compensation, namely, reduction in response, it is virtually impossible for video CDs to realize such reproduction control as changing menu items synchronizing with the moving picture images. In other words, it is impossible to have a close correspondence between images and reproduction control. For example, in FIG. 1, if a detective meets a suspicious-looking man, a menu asking the user to select an option is displayed according to the change in his face.
Second problem is that the reproduction cannot be controlled by a combination of a past result of the user selection and a current result of the user selection. For example, imagine a case of a teaching material where questions are displayed one by one and the points obtained by the user with correct answers are counted up, after all the questions complete, the user is judged as passed the examination if the user's point has exceeded a certain point. In video CDs, branch targets cannot be changed according to the past result of the user selection. Therefore, it is impossible to achieve such an interactive software title as changing the branch target according to the point for a plurality of questions.
Moreover, for a multi-story detective story, unexpected story development and different stories are required so that the user can repeatedly be interested in the story. However, if a menu item corresponds to only one story development, the user will soon learn the branch target. That is, in the beginning, the user may have an unexpected feeling for the story development, but soon will learn the story development in several repetitions. Then, the user will lose interest in the title. In the software title of the detective story, if item "glasses" is selected, the control always branches to reproduction route #3. It is desired that sometimes the control branches to another route by reflecting the past user selections for the actions of the detective. If the selection of item "glasses" always leads to reproduction route #3, the user is accustomed to the story development after playing the interactive software title several times.